I've been working this for the past month getting ready for my test on Tuesday. I purchased:
-Modern Refrigeration and Air conditioning, 18th edition, text book
-Dewalt HVAC Technician Certification Exam Guide, 2nd edition
-ACCA 4 disc pack on A/C Service and Installation
Get your pro status on these forums and use their educational section....there is an incredible wealth of knowledge here with these guys.